In the mind
The reason I got into shooting was my doctor told me to get a hobby.
Distraction is a very useful tool and when you have mastered that tool , it can be used for many different situations.
My Advice would be to stop trying to fix it.
You have already diagnosed yourself by saying the more you think about it the worse it gets and after the damage is done it goes away.
Just do the basics exercise for breath control , avoid too much caffeine for a couple of days before a shoot and don't eat loads of sugar filled foods before a shoot.
Find a focal point like Rob said technique or maybe focus on trying to read the wind, the harder you try to beat this the closer it will get to the forefront of your mind.
It will take a while trust me but one day you'll notice that it's not happening any more , then you will understand what I mean about the "tool" .
About as much use at field target , as a life guard at the Olympic swimming pool.